is timeline relevant when starting a logical slot?

I get an error when trying to include timeline in the start config for a logical slot. The postgres docs dont seem to mention anything about timeline with regard to logical, they do however for physical.

#### docs:
```
START_REPLICATION SLOT slot_name LOGICAL XXX/XXX [ ( option_name [ option_value ] [, ...] ) ]
vs
START_REPLICATION [ SLOT slot_name ] [ PHYSICAL ] XXX/XXX [ TIMELINE tli ]
```

#### result of pglogrepl.IdentifySystem()
```
{"level":"info","msg":"SystemID: 6938529628705222694 Timeline: 1 XLogPos: 0/1765F08 DBName: postgres","time":"2021-03-11T22:43:05Z"}
```

#### sql print from [here](https://github.com/jackc/pglogrepl/blob/master/pglogrepl.go#L260)
```
sql: START_REPLICATION SLOT regression_slot LOGICAL 0/1765FF0 (TIMELINE 1)
```
#### error
```
failed to start replication: ERROR: syntax error (SQLSTATE 42601)
```

#### possible solution? Should [this](https://github.com/jackc/pglogrepl/blob/master/pglogrepl.go#L247) be changed to:
```
if options.Timeline > 0 && options.Mode == PhysicalReplication {
```

Start in pglogrepl.go around the option handling at line 247 and SQL assembly at line 260, then compare the logical and physical START_REPLICATION syntax shown in the issue. Done means logical replication no longer emits the TIMELINE option, while physical replication retains its existing timeline behavior; verify the resulting SQL against PostgreSQL syntax.

Written by the indexing model from the issue text.